In general, the DNS enables translation of domain names to Internet Protocol (IP) addresses. Such translation makes it possible to attach easy-to-remember domain names (e.g., “domainname.org”) to difficult-to-remember IP addresses (e.g., “200.140.130.120”). A detailed description of conventional DNS is provided in documents entitled “RFC 1034 —DOMAIN NAMES—CONCEPTS AND FACILITIES” and “RFC 1035—DOMAIN NAMES—IMPLEMENTATION AND SPECIFICATION,” both by P. Mockapetris, November 1987, the teachings of which are hereby incorporated by reference in their entirety.
Some hosts have dynamically provided IP addresses provided by Dynamic Host Configuration Protocol (DHCP) servers. A host having a dynamically provided IP address may also have a domain name. However, since dynamically assigned IP addresses are generally only valid for finite amounts of time, the IP address associated with a particular domain name may change from time to time. In order to keep DNS current in a DHCP environment, DHCP hosts typically register and dynamically update their resource records (RRs) with authoritative DNS name servers whenever their IP address changes. Such operation reduces the manual administration burden of zone records, i.e., master files which are managed by the authoritative DNS name servers. A detailed description of the conventional DNS update process is provided in a document entitled “RFC 2136-DYNAMIC UPDATES IN THE DOMAIN NAME SYSTEM (DNS UPDATE)”, by P. Vixie et al., April 1997, the teachings of which are hereby incorporated by reference in their entirety.
Primary authoritative DNS name servers may accept changes to the DNS tables and respond to DNS resolution requests, while secondary authoritative DNS servers do not accept changes to the DNS tables via Dynamic DNS updates. Since there is ordinarily only one primary authoritative DNS server per DNS zone, if the primary server goes down, Dynamic DNS updates will not be able to proceed. This can be problematic for protocols requiring high availability, such as VoIP and Mobile IP. In one conventional system (hereinafter the Multi-master approach), high availability is achieved by utilizing multiple primary authoritative DNS servers which all write to a common Lightweight Directory Access Protocol (LDAP) distributed database. Similar systems use Active Directory as this LDAP distributed database. Active Directory is a trademark of Microsoft Corporation or Redmond, Wash. The LDAP distributed database allows the primary servers to periodically communicate with each other to synchronize their databases using multi-master replication. In another conventional system (hereinafter the Central DB approach), high availability is achieved by allowing secondary authoritative DNS servers to accept DNS changes. In this approach, each DNS server to accept a change temporarily stores the change in its database, and propagates the change to a common database that implements the change, and propagates the change down to all the primary and secondary DNS servers. Similar systems use an Oracle® database. Oracle® is a registered trademark of Oracle Corporation of Redwood Shores, Calif. Once the change propagates down, the temporary change is deleted.